In recent years, heavy lift cranes have been made capable of lifting ever greater loads at increased heights and lifting radii. Also, the question of economy is always present and with larger, inherently more expensive devices, the need for additional equipment to assist in erection and disassembly and the tyeing up of the apparatus in a configuration which is not fully utilized becomes increasingly costly.
While a number of factors enter into determining crane capacity, a basic limitation arises from the fact that, inevitably, the weight of the crane and its load must be transferred to the earth in some stable fashion and, if rotation of the load is desired, the crane-earth connection must be made stable through the arc of crane rotation.
A significant increase in crane capacity was achieved by providing a self-propelled crane with the support ring and extended boom carrier disclosed and claimed in U.S. Pat. Nos. 3,485,383; 3,878,944 and 4,194,638 assigned to the assignee of the present invention. In the design disclosed in these patents, the weight of the crane and its load is transferred to the ground through a large diameter, track-like ring. As shown in these patents, and as practiced commercially for some years, the support ring is either blocked into place by timbers fitted and wedged beneath and completely around the ring or is supported by a plurality of jacks spaced around the periphery of the ring.
Further refinements in ring supported cranes are disclosed in U.S. Pat. Nos. 4,042,115, 4,103,783 and 4,195,740 as well as in copending application Ser. Nos. 058,284 and 058,285, both filed July 17, 1979, now abandoned; and all of which are assigned to the assignee of the present invention. These patents and applications disclose inter alia that a separate transporter mechanism may be run in and out of an otherwise stationary ring supported crane in order to move that crane between different locations or job sites, that the ring may be mounted on a support frame on a single transporter or the ring may be mounted on fore and aft transporter mechanisms to support the heavy boom and counterweight loads.